1. Field of the Invention
The present invention relates to an apparatus and method for generating alkali metal hydroxide, molecular halogen, and hydrogen. The invention relates more specifically to an apparatus and method for the solar-augmented electrolytic production of the aforementioned products from a concentrated aqueous solution of alkali halide.
The subject matter of this patent application is related in part to pending patent application Ser. No. 07/526,435, filed May 22, 1990, pending which is a continuation-in-part of patent application Ser. No. 07/393 filed Dec. 14, 1987, abandoned, which in turn is a continuation-in-part of Ser. No. 804,518 filed Dec. 4, 1985, abandoned.
2. Description of the Related Art
The electrolysis of an aqueous solution of alkali chloride to produce hydrogen, chlorine, and caustic soda is a well-known and valuable industrial process. Recent major advances in the chlor-alkali industry include more efficient solid-state rectifiers, larger and higher capacity electrolytic cells, dimensionally stable anodes to replace graphite, and cation exchange membranes to replace the traditional asbestos diaphragms.
Despite these advances, the industry is still faced with the serious problem of contending with the substantial electrical power demand associated with the process. The extent of this demand is evidenced by the fact that 0.5% of all the electric power generated annually in the United States is utilized by the chlor-alkali industry.
The maximum amount of chlorine and caustic soda that can be produced using either mercury- or diaphragm-cell technology is determined by the total number of ampere-hours of direct current electricity consumed. The corresponding energy consumption is a direct, linear function of the cell working voltage, with the greatest contributor to the cell voltage being the energy required to meet the thermodynamic potential.
Prior art efforts to reduce the electrical power requirement have focused on the electrolytic cell itself, rather than the electrolyte employed therein. The present invention, however, reduces the electrical power requirement by using radiation to activate photo-sensitive transition metal hexahalide ions, which reduces the electrolysis electrode potential.
The crystal field and electron transfer spectra of Group VIII transition metal complexes have been described by C. K. Jorgensen, Acta Chimica Scandanavica. Vol. 10, No. 4 (1956), 500, 518; Vol. 11, No. 1 (1957), 151, 166. A description of the photochemical effect on transition metal complex ions when subjected to radiation at visible wavelengths is provided in H. B. Gray, Science, Vol. 214 (1981), 1201.